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The integrated 21 cm H I emission profile of a galaxy encodes valuableinformation on the kinematics, spatial distribution, and dynamical state of itscold interstellar medium. The line width, in particular, reflects the rotationvelocity of the galaxy, which, in combination with a size scale, can be used toconstrain the dynamical mass of the system. We introduce a new method based onthe concept of the curve of growth to derive a set of robust parameters tocharacterize the line width, asymmetry, and concentration of the integrated H Ispectra. We use mock spectra to evaluate the performance of our method, toestimate realistic systematic uncertainties for the proposed parameters, and tocorrect the line widths for the effects of instrumental resolution andturbulence broadening. Using a large sample of nearby galaxies with availablespatially resolved kinematics, we demonstrate that the newly defined linewidths can predict the rotational velocities of galaxies to within an accuracyof $\lesssim 30$ km s$^{-1}$. We use the calibrated line widths, in conjunctionwith the empirical relation between the size and mass of H I disks, toformulate a prescription for estimating the dynamical mass within the HI-emitting region of gas-rich galaxies. Our formalism yields dynamical massesaccurate to $\sim 0.3$ dex based solely on quantities that can be derivedefficiently and robustly from current and future extragalactic H I surveys. Wefurther extend the dynamical mass calibration to the scale of the dark matterhalo.

On the Determination of Rotation Velocity and Dynamical Mass of Galaxies Based on Integrated H I Spectra